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DEPARTMENT OF COMMERCE 



Scientific Papers 



OF THE 



Bureau of Standards 

S. W. STRATTON, Director 



No. 321 

thermal expansion of alpha and of 

beta brass between and 600° c, in relation to the 

mechanical properties of heterogeneous 

brasses of the muntz metal type 

BY 

P. D. MERICA, Associate Physicist 

and 

L. W. SCHAD, Assistant Physicist 

Bureau of Standards 



ISSUED MAY 9, 1918 




PRICE, 10 CERTS 

Sold only by the Superintendent ot Documents, Government Printing Office, 
Washington, D. C. 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1918 



DEPARTMENT OF COMMERCE 



Scientific Papers 



OF THE 



Bureau of Standards 

S. W. STRATTON, Director 



No. 321 

THERMAL EXPANSION OF ALPHA AND OF 

BETA BRASS BETWEEN AND 600° C, IN RELATION TO THE 

MECHANICAL PROPERTIES OF HETEROGENEOUS 

BRASSES OF THE MUNTZ METAL TYPE 

BY 

P. D. MERICA, Associate Physicist 

and 

L. W. SCHAD, Assistant Physicist 
Bureau of Standards 



ISSUED MAY 9, 1918 




PRICE, 10 CENTS 

Sold only by the Superintendent of Documents, Government Printing Office, 

Washington, D. C. 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1918 



K 



<\ 



o 




\9 



D. of D. 
jun I 1918 



THERMAL EXPANSION OF ALPHA AND OF BETA 
BRASS BETWEEN AND 600° C, IN RELATION TO 
THE MECHANICAL PROPERTIES OF HETERO- 
GENEOUS BRASSES OF THE MUNTZ METAL TYPE 



By P. D. Merica and L. W. Schad 



CONTENTS 

Page 

I. Introduction 571 

II. Thermal expansion of alpha and of beta brass : 574 

1 . Preparation of alloys 574 

2 . Measurement of expansion 574 

3 . Results and discussion .' 578 

4. Local "grain stresses" due to differences in thermal expansion. . . 586 

III. Effect of certain heat treatments on mechanical properties of 60 140 brass. . 587 

IV. Conclusion 589 

I. INTRODUCTION 

In the course of recent investigation of the cracking or fractur- 
ing of brass articles of the type composition, 60 per cent copper 
and 40 per cent zinc, it has been possible to give adequate expla- 
nation for failure in most of the individual cases. These failures 
have been ascribed to excessive initial or service stress in conjunc- 
tion with corrosion, or to the improper execution of the forging 
operation by which the article was formed. A number of instances 
of cracking in brass of this type have, however, come to the atten- 
tion of the authors, for which these explanations can not be appli- 
cable. Such an instance is the following: 

A ^-inch diameter naval brass hook bolt, which had been heated 
to "cherry red" and quenched in warm water, was used in the 
support of a strainer plate in a water-filter plant, under a tensile 
stress of from 10 000 to 15000 pounds per square inch. After 
about 60 days it broke off, with practically no elongation. There 
was little initial stress in this bolt, and the load stress was not 
above the proportional limit; the subsequent cracking of the 
bolt appears, therefore, rather mysterious 

571 



572 



Bulletin of the Bureau of Standards 



[Vol. 14 



Several naval brass rivets have been examined which had frac- 
tured at the shoulder, under a tensional stress no greater than 
that caused by the restrained thermal expansion of the rivet 
after heating. 

These cases have been described more fully. 1 

In all of these instances, in which the usual mode of explana- 
tion of cracking has failed, it was discovered that the brass article 



1100 


- 












Equilibrium 




1000 
900 

800 






diagram of 
Copper-Zino 
all oys 














alpha \ \ bet 


a / 


; ^- 


•8 

3 

J? 700 

o 
o 


- 




V 




n 600 

<D 

to 












S 500 


" 










•H 










■ 


§ 400 

+> 

d 
Pi 












a. 300 
a 

5 

n 


~ 




















200 


- 










100 




a 
i i 1 


b 

i 


i i l 






10 20 30 40 50 60 70 






Per cent Zinc by Weight 



Fig. i. — Portion of equilibrium diagram of copper-zinc alloys 

had been subjected, at some time, to a very rapid cooling or 
quenching. Since the 60 : 40 (60 per cent copper and 40 per cent 
zinc) alloy is heterogeneous in structure, consisting of the two 
constituents, alpha and beta, in approximately equal proportions, 
the thought occurred to the authors that local stresses between the 
alpha and the beta constituents, caused by their unequal thermal 
expansion, might be developed during its rapid cooling. It was 



1 Merica and Woodward, Bureau of Standards, Technologic Paper No. 82, 1916; Trans. Am. Inst. Metals, 
9, 298, 1915. 



Merica~\ 
Schad J 



Thermal Expansion of A Ipha and Beta Brass 



573 



with the idea of obtaining some information on this point that 
the work described below was undertaken, with the purpose of 
determining the difference between the unit thermal expansion 
values of the two constituents, alpha and beta, of 60 : 40 brass. 

Apparently there has been, hitherto, no investigation along this 
line, either with brass or with other heterogeneous alloys. Some 
determinations 2 have been made of the thermal expansion of 
brass of different compositions, particularly at ordinary temper- 
atures. 

It was desired in this work to compare the thermal expansion 
of alpha and beta brass 3 of compositions which are normally in 
equilibrium with each other at ordinary temperatures. In the 
case of the pure copper-zinc alloy, compositions such as those at 
a and b in Fig. 1 were chosen; in a slowly cooled alloy of any 
intermediate composition the concentrations of copper or zinc in 
the alpha and in the beta phases will be those given by these 
points. The preparation of homogeneous alloys of these com- 
positions is not possible in general without appropriate heat treat- 
ment. The cast alpha brass must be annealed for some time at 
approximately 500 C and slowly cooled ; the beta alloy may require 
to be quenched from above the transformation range and drawn 
to relieve stresses. 



TABLE 1. — Composition of Brass Samples 



Number of alloy 


Chemical analysis 


Phase 


Copper 


Zinc 


Tin 


Lead 


Iron 


2151 


Percent 
65.6 
54.5 
53.5 
54.7 
65.3 
67.2 
64.6 
55.5 


Per cent 

32.9 
43.9 
45.6 
44.5 
34.5 
32 
35.4 
44.5 


Per cent 

1.3 
1.3 
.9 
.7 
.23 
.7 
.06 
.07 


Per cent 

0.2 

.1 

Trace 

.1 
.2 

.1 

.04 

.05 


Per cent 

0.1 

.2 

Trace 

.1 

Trace 

.1 

<.04 

<.04 


Per cent 

Alpha 

Beta 


216 a 


250 a 


Alpha 
Do 


252 a 


256 a 


Beta 


257 a 


Do 


259 & 




261 b 


Beta 







a These samples were east from some remeltecl copper and Horsehead spelter. 

I' These samples were cast from electrolytic copper and Horsehead spelter; they contained, therefore 
only slight amounts of impurities. 

' Dittenberger, Zeit. Ver. deutsch. Ing., 16, p. 1532, 1902; Bcnoit, Journ. de IMiys., S, p. 471, 1S89; 
Hciming, Ann. d. phys., 22, p. 631, 1907; Price, Trans. Am. Int. Metals, X, p. 133, 1916. 

3 Hereafter the terms "alpha" and "beta" will be used to denote the alpha and beta phases, respectively . 
of brass. 



574 Bulletin of the Bureau of Standards ivei.14 

TABLE 2. -Heat Treatment of Alpha and Beta Alloys After Casting 



Specimen 


Time of 
heating 


Temper- 
ature 


Cooling 


Time of 
heating 


Temper- 
ature 


Cooling 


Time of 
heating 


Temper- 
ature 


Cooling 


215A 

216C 

215C 

250A 


Minutes 
10 
15 

10 

45 

45 

45 

45 
240 
240 
240 
240 

15 

15 


°C 

700 

750 

700 
350-450 
350-450 
350-450 
350-450 

600 

600 

600 

600 

750 

750 


f-c 
q-w 
f-c 
f-c 
f-c 
f-c 
f-c 
f-c 
f-c 
f-c 
f-c 
f-c 
q-o 


Minutes 
60 
60 
60 


°C 

600 

100-150 

600 


f-c 
f-c 
f-c 


Minutes 
180 
10 
180 


•c 

600 

300-400 

600 


f-c 
f-c 
f-c 


250B 












252A 








252B 








256A 








256B 








257A 






257B . 






f-c 




259A 









261F 


120 


325 









f-c indicates furnace cooled. 

q-w indicates quenching in water. 

q-o indicates quenching in oil. 

II. THERMAL EXPANSION OF ALPHA AND OF BETA BRASS 
1. PREPARATION OF ALLOYS 

The samples for the measurements were cast in chill molds, 
heat treated in order to produce a homogeneous, stress-free alloy, 
then machined and tested. 

The specimens 259 and 261 were made of pure electrolytic 
copper and Horsehead zinc; the others were made of some re- 
melted copper, together with Horsehead zinc and Straits tin. 
These samples, unfortunately, contained some lead and iron. The 
chemical analyses of the samples are given in Table 1 . 

After casting, the alpha brasses were annealed and the beta 
brasses treated as indicated in Table 2 in order to homogenize the 
alloy and relieve it of stress. The specimens were heat treated 
until they were homogeneous as determined microscopically; this 
required several periods of heating for some specimenas. An idea 
of the homogeneity of the alloys may be obtained from the micro- 
graphs, Figs. 6 to 11. 

2. MEASUREMENT OF EXPANSION. 

The thermal expansivity measurements were made in special 
apparatus designed and built at the Bureau of Standards for the 
purpose of obtaining good temperature uniformity and high 
accuracy in measuring length changes. 



Merica~\ 
Schad J 



Thermal Expansion of Alpha and Beta Brass 



575 



The specimens tested to 500 C or over were heated in air in an 
electric furnace in which the temperature as determined by dif- 
ferential thermoelements was uniform to o.i° C throughout the 
entire chamber containing the specimen. The absolute tempera- 



.015 



.012 



.005 



.ocs 



Linear Expansion 

of 

Alpha and of Seta 

Brass 

259 . . alpha brass 

261 .. beta brass 




-Q1Z 



T«0* 



Deviation of observed 
iTiear expansion ( dl/^l) 
from the quadratic 
equat ions : 



r^Ti 



dl/1 = ( 16. 021; + .0067* ) 10" 6 

261 
dl/l~^T~18.10t + .01312t*) 10" 6 




200 400 600 

Temperature in Degrees Centigrade 



Fig. 2. — Expansion curves of brass 

tures were determined by a carefully calibrated platinum platinum- 
rhodium thermoelement. 

The tests to 300 or less were made in an oil bath in which the 
temperature variation was perhaps less than o.i°C over the entire 
specimen. In this case the absolute temperatures were determined 



576 



Bulletin of the Bureau of Standards 



[Vol. 14 



with a copper-constantan thermoelement immersed in the oil at 
the side of the specimen. 

The length changes were determined with a special comparator, 
consisting of two microscopes rigidly clamped on an invar bar at a 




Fig. 3. — Expansion curves of brass 

distance from each other equal to the length of the specimen and 
so arranged that they could first be sighted on a standard-length 
bar kept at a constant temperature and then on the 1 mil wires 
dropped over the ends of the specimen under test. 4 

* Journal of the Washington Academy of Sciences, 11. P. 248; 1913. 



_M 



Merica 
Schad 



Thermal Expansion of Alpha and Beta Brass 



577 



The length changes measured in this way are accurate to about 
±0.001 mm, which on a specimen of 300 mm long (the standard 
length of the specimen) would be ± 0.0003 P er cent. 



Fig 




-Expansion curves of brass: Q=points taken on heating; %= points taken on 

cooling 



For specimens heated in oil to 300 or less each test was com- 
pleted in about five hours; the test to 6oo° C in the air furnace 
was completed in from three to five days. Experience seemed to 
show that the rapidity with which the test was made had little 
or no effect upon the behavior of the specimen. 

'27819°— 18 2 



578 



Bulletin of the Bureau of Standards 



l Vol. 1. 1 



3. RESULTS AND DISCUSSION 

The data are given in Figs. 2 to 5, in which is shown in each 
case the actual unit linear thermal expansion (linear expansion 
per unit length) and also the deviation of this observed expansion 
from that computed from a quadratic equation, which in each 
case best fits the series of observations. 

The curves for alpha are continuous in each case up to 6oo° C, 
whereas the transformation of beta into beta prime is readily 



5 

c? .006 



.004- 



.000 



Linear Thermal Expansion 

of 
Alpha and of Beta Brass 

257 . alpha brass 

250 . . beta brass 




The points marked ( ><. ) 
represent measurements 
made on a second " run " 



•r0e4- 



100 200 300 

Temperature in degrees centigrade 



Fig. 5. — Expansion curves of brass 

seen in the change in the slope of the beta curve at from 450 to 
460 C. The first terms of the quadratic equation representing 
the thermal expansion are very nearly equal, although with a 
high tin content the value for beta becomes higher. The second 
term of the equation for alpha is, however, consistently lower 
than that of the beta; indeed, it is only approximately one-half 
of the second term of the beta equation. Thus, although from 



Merical 
Schad J 



Thermal Expansion of Alpha and Beta Brass 



579 



o° to about 300 C the expansions of alpha and beta brass are 
almost equal, beyond this temperature and up to 460 C the expan- 
sion of the beta becomes almost twice that of the alpha. This is 
shown in Table 3. Above the transformation temperature the 
curve of the expansion of the beta is almost linear and runs nearly 
nearly parallel to that of the alpha. 

The quadratic equations best fitting the observed expansions 
are given on the figures. It is to be noted: 

1. That the portion of the beta curve up to 460 C would be 
better fitted with a cubic curve. 

2. That above this transformation point the curve is approxi- 
mately linear (to 600 ° C) and might be represented as follows: 

TABLE 3. — Expansion of Brass Over Different Temperature Intervals 



Specimen 


Unit linear expansion per degree centigrade between — 


20 and 100° 


100 and 200° 


200 and 300° 


300 and 400° 


400 and 450° 


500 and 600° 


215A; alpha 

216C; beta 


19.2X10-6 
21.6X10-6 
20.1X10-6 
22.8X10-6 
18.7X10-6 
22.8X10-6 
20.0X10-6 


20.0X10-6 
21.8X10-6 


22.0X10-6 
22.8X10-6 


22.5X10-6 
29.6X10-6 


23.5X10-6 
35.0X10-6 


24.5X10-6 
30.5X10-6 


250A; alpha 




252A; beta 


19.4X10- 6 
20.0X10-6 
22.2X10-6 
21.0X10-6 


23.5X10-6 
22.0X10-6 
21.9X10-6 
23.6X10-6 


27.5X10-6 
22.5X10-6 
22.2X10-6 
28.0X10-6 


39.2X10-6 
23.0X10-6 
23.4X10-6 
35.0X10-6 


26.9X10-6 


256A; alpha 


23.7X10" 6 


259A; alpha 


23.6X10-6 


261F; beta 


27.0X10- 6 







For brass No. 261 rf/=26.5Xio- 6 t 
T 

For brass No. 252 dl=2j.gXio- R t 
I 

For brass No. 2i6'<W=25.2Xio- 6 t 
T 

The second term of a quadratic fitting these curves would be 
small (and negative in value for No. 261). 

Very interesting are the deviations observed by subtracting the 
values computed from the quadratic equations noted in the 
curves (Figs. 2 to 5) from the observed expansions; these, are 
plotted in the same figureon a larger scale. It is seen that the 
deviation of the alpha brass is at first zero, then at about 100 to 
150 it becomes positive, attaining a maximum at from 300 to 350°, 
falling off thereafter to o at about 500 ° and becoming negative. 
The beta brass pursues almost the reverse course; the deviations 
attain a negative maximum at about 350 , rise to a sharp posi- 
tive maximum at about 400 , and drop again rapidly. These 
deviations are quite regular and occur in all of the samples. 



sSo 



Bulletin of the Bureau of Standards ivoi.14 




4 



Fig. 6. — .\o. 215, alpha brass, cast and annealed. Xioo 







\ 



Fig. 7. — No. 216, beta brass, cast and annealed. Xioo 



sckad"] Thermal Expansion of Alpha and Beta Brass 581 




Fig. 8. — No. 256, alpha brass, cast and annealed. \ioo 




Fig. 9. — No. 252, beta brass, cast and annealed. Xioo 



5»2 



Bulletin of the Bureau of Standards 



[Vol. 14 





■ : 














•* • 












































. 


I 











Fig. io. — So. 2jq, alpha brass, cast and annealed. X-ft 




Fig. ii. — No. 261, beta brass, cast and annealed. Xioo 



- — 



Hta 



M erica] 
Schad J 



Thermal Expansion of Alpha and Beta Brass 583 




Fig. 12. — No. 261, beta brass, after heating to 600° C. Xioo 




Fig. 13. — No. l6g Q, naval brass, quenched. X500 



584 



Bulletin of the Bureau of Standards 



\V,d.i 4 




Fig. 14. — No. i6g R, naval brass, quenched and drawn. X500 







*i. ' 






Fig. 15. — No. l6g V, naval brass, slowly cooled. X5C 



¥cimT~\ Thermal Expansion of Alpha and Beta Brass 585 

They are related closely to the transformation point in the case of 
the beta brass. 

In the case of the alpha brass a slight permanent elongation 
was noticed in some cases after heating to 6oo° C and cooling, 
whereas in the beta brass a shrinkage always took place. This 
shrinkage is most marked in specimen 250, Fig. 5, heated to 
300 C ; the corresponding alpha brass showed no change in length 
whatever. The second determination on the sample 250, indi- 
cated in Fig. 5, gave an expansion coinciding exactly with the 
" down " curve of the first. 

It may be noted that some precipitation of alpha took place 
in the sample 261 upon heating between 400 and 600 ° C; this is 
shown in the micrograph, Fig. 12, showing the structure of the 
thermal expansion specimen after a 6oo° C heating. 

This precipitation of alpha (which has a slightly different density 
than beta) would alter the observed coefficient through the 
temperature range of its precipitation. 

Thus, if 

V = specific volume of the alloy 

V a = specific volume of the alpha constituent 

Vp = specific volume of the beta constituent 

m = fraction of alpha by weight, 

then V = mV a + (i-m) Vp. 

dv dV a T7 dm , s dV s T / dm 

di =m -dT + V * dt +{l - ni) -df-- V '-Tt 

dm /rT TZ . /dV„ dV g \ . dV s 



CK.^.-^-^gt 



dt v a p/ \ dt dt ) dt 

Measurements showed the densities at ordinary temperatures 
of 259 (alpha) and 261 (beta) to be as follows: 



259 8.294 

261 8.226 



(v-^—\ 

\ density/ 



If it is assumed that 5 per cent of alpha has been formed be- 
tween 460 and 480 C, 






AV 
AT 



0.05 / / I \ dV „ , dV& 

= [ ]A .-^ = - 2.4S X IO _6 H rp 

20 V8.294 8.226/^ di ^° dl 

1 dL 1 dV . o , /- \ n 
. .' .r-r=- 11 =(-0.82 + 26.5) io-» 

L L i> dL 



,S*S6 Bulletin of the Bureau of Staiulards iv«i. u 

The precipitation of alpha has therefore a small but appre- 
ciable effect on the thermal expansion coefficient. 

4. LOCAL "GRAIN STRESSES" DUE TO DIFFERENCES IN THERMAL 

EXPANSION 

It is much beyond the scope of this paper to attempt a dis- 
cussion of the magnitude and distribution of stresses arising 
during the cooling of a heterogeneous aggregate of particles of 
different coefficients of thermal expansion. A particle imbedded 
in a homogeneous mass having a greater unit thermal expansion 
than it has, will be, after rapid cooling, essentially in hydro- 
static or isotropic compression. The ground mass surrounding 
it will, at the surface of division, be subject to a system of tan- 
gential tensional stresses parallel to it. The magnitude and dis- 
tribution of these stresses will depend on the size, shape of the 
imbedded particles and their distances apart. 

One may gain a very rough idea of the magnitude of such 
stresses by assuming that the two constitutents are in the form of 
bars rigidly clamped parallel to each other. When the tem- 
perature of such a duplex bar is lowered there will be in each 
constitutent bar (if of equal cross section) a stress equal to 

AdL E 
L 2 

A/7 T 

where — y— — difference in thermal expansion per unit length be- 
tween the constitutents. 

E = modulus of elasticity. 

Such stresses are calculated on the basis of E equal to 15 x 
io" pounds per square inch and are given in Table 4. The 
values may be considered as representing the tensional stress in 
the beta and the compressional stress in the alpha bar which 
remain after cooling rapidly from the temperatures indicated. 
The reverse stresses would be temporarily caused by rapid heating. 
As the amount of beta in a brass is increased, the average stress 
from this cause in the beta would decrease; one would expect, 
therefore, other things being equal, to find a greater effect of such 
stresses in an alloy of beta than in one such as manganese bronze; 
a quenched alloy with alpha grains surrounded by beta envelopes 
should show most noticeably any effect of tensional stress in the 
beta constitutent. 






■^ ' 



Mericdl 
Schad J 



Thermal Expansion of Alpha and Beta Brass 



5«7 



It is noted that the development of stress, due to unequal 
thermal expansion, during the cooling of a 60:40 brass, is greatest 
within the temperature range from 300 to 500 ° C, at which 
experience has indicated, annealing and relief of stresses take 
place fairly readily. One may assume, therefore, that during 
slow cooling of such an alloy from 500 to 600 °, the alloy con- 
stitutents yield locally under the stresses produced through the 
range 600 to 300 . Below 300 the contraction of the two con- 
stitutents is almost equal. During rapid cooling, however, the 
time may not be sufficient to allow of the local yielding to any 
extent of the consitutents ; they arrive at ordinary temperature, 
therefore, in a state of stress described above. 

TABLE 4. — Calculated Stresses Due to Difference in Thermal Expansion Between 

Alpha and Beta Brass 





For 

215 and 
216B 


For 

256 and 
252B 


For 

259 and 
261B 




0. 00050 
3750 
0.0012 
9000 
0. 0022 
16 500 
0.0022 
16 500 


1 
0.0005 n nnnjfi 




3750 
0.0010 

7500 
0.0021 
15 800 


1950 




0. 00075 




5600 




00162 




12 200 




0. 00190 






14 200 









o Assuming two bars, one of A and one of B, rigidly clamped and heated from o° C to the temperature 
noted, or cooled through this range; E is assumed to be is x io 6 pounds per square inch. 



III. EFFECTS OF CERTAIN HEAT TREATMENTS ON 
MECHANICAL PROPERTIES OF 60:40 BRASS 

Some experiments were undertaken with a view to ascertaining 
directly whether the "grain" stresses described above exerted 
an appreciable effect upon the properties of the brass. 

Six-inch lengths of drawn brass i-inch diameter rods 164, 169, 
171, 173, and 1 75 r> of the compositions and properties given in 
Table 5, were given the heat treatments described in Table 6, 
which consisted largely in the heating of the specimen to various 
temperatures between 400 and 6oo° C, and the quenching of them 
in water or oil. The samples were then submitted to the mer- 
curous nitrate test. This test indicates the presence of initial 
stress of significant extent caused by drawing or working brass. 
None of the samples cracked during the quenching or in the test. 

6 Described more fully in Tallies j, i, and s <>( Bureau oi Standards Technology Papei No. 82. 



588 



Bulletin of the Bureau of Standards 



[Vol. 14 



A few 1 inch diameter samples of naval brass and of Muntz 
metal were quenched or slowly cooled from 500 or from 400 C. 
These were then machined to 0.505 -inch diameter and tested 
in tension. The results of these tests are shown in the Table 7. 
Without exception the quenched samples have a slightly lower 
proportional limit and a higher tensile strength than the samples 
which were slowly cooled from the same temperature or were 
quenched and drawn back to 400 C in order to relieve the local 
stresses. ' 

It must be observed that the full effect of differential grain 
stresses on the mechanical properties of a brass might not be 
developed except when the brass was at the same time under 
additional tensional stress. The latter would increase the local 
tensional stresses and diminish the local compressional stresses 
such that an incipient local surface crack might develop through- 
out the brass. Information on this point could be obtained 
from the results of corrosion tests under stress such as are being 
conducted at present at the Bureau. 

In the case of the naval brass the samples heated to 400 or 
thereabouts suffered in ductility, a fact which was readily ex- 
plained by a miscroscopic examination of such samples. At 
that temperature the hard delta constitutent forms at the edge 
of the beta grains. This can be seen in the micrographs Figs. 
13 to 15. At higher temperatures the quenched specimens did 
now show anv delta. 

TABLE 5. — Chemical Composition of Brasses Which Were Heat Treated and Tested 

in Tension 





Material 


Chemical analysis 


Physical properties 


Num- 
ber 


Copper 


Zinc 


Tin 


Iron 


Ultimate 
strength 


Elonga- 
tion in 2 
inches 


164 




Per ct. 
61.1 


Per ct. 
38.5 
37.5 
40.2 
39.9 
40.9 


Per ct. 


Per ct. 


lbs./in.2 
72 000 
83 000 
80 000 
100 500 
77 000 


Perct. 

a 16 


169 
171 
173 

175 




61.2 
59.4 
56.8 
57.5 


1.2 


13 




21 




1.6 
1.0 


1.3 
.6 


9 




27 



o In 3 inches. 



Schad a ] Thermal Expansion of Alpha and Beta Brass 589 

TABLE 6. — Heat Treatment of Brass Samples Submitted to Mercurous Nitrate Test 



Specimen 



Heat treatment 



164A. 
164B. 
164C. 
164D. 
169C. 
169D. 
169K. 
169L. 
169M 
169N. 
1690. 
169P. 
169T. 
169W 
171F. 
171G. 
171K. 
175A. 
175B. 
171C. 



1 hour at 430°, water quenched. 

\\ hours at 430°, oil quenched. 

1| hours at 480°, water quenched. 

1J hours at 480°, oil quenched. 

l\ hours at 480°, water quenched] _,„. „„„. . . 

2 H (750°-830°, water quenched. 

1J hours at 480°, oil quenched. . .J 

20 hours at 625°, water quenched. 

Do. 

Do. 

[tested. 

annealed 1 hour at 330° 
20 minutes at 625 to 500°, water quenched. 
20 minutes at 400°, quenched. 
40 minutes at 400°, furnace cooled. 
20 minutes at 500°, water quenched. 
20 minutes at 500°, 20 minutes at 440°, water quenched. 
20 minutes at 500°, 20 minutes at 440°, furnace cooled. 
30 minutes at 445°, water quenched. 
30 minutes at 440°, oil quenched. 
1| hours at 480°, water quenched. 



30 minutes at 620-600°, water quenchcdJ 

a 



TABLE 7. — Mechanical Properties of Heat-Treated Naval Brass and Muntz Metal 








Heat treatment 


Physical properties 


Speci- 
men 


Ultimate 
strength 


Proportional 
limit 


Elastic 
modulus 


Elonga- 
tion in 2 
seconds 


Reduc- 
tion of 
area 




[30 minutes at 600-620° tested 


Lbs./in." 

59.7x10° 

56.6 
63.2 
61.6 
59.3 

60.4 
58.8 

57.7 


Lbs./in.* 

14.0x10 s 

18.0 
16.5 
20.0 
16.2 

14.0 
12.5 

16.2 


Lbs./in.a 

14.4x10° 

16.0 
14.3 
14.8 
13.9 

14.3 
13.7 

13.9 


Per cent 
34.5. 

21.0 
26.5 
30.0 
53.0 

53.0 
54.0 

54.5 


Per cent 

33 


169Q 


] Followed by 20 minutes at 500°, 


21.6 


169S 
169V 
171D 

171E 


15 minutes at 428°, water quench 

20 minutes at 428°, furnace cooled 

(20 minutes at 500°, | (2 seconds at 
< water quench. [ \ 400°. 

| (tested 


25.0 
25.1 
57.1 

57 6 


171H 
171J 


20 minutes at 500° (water quench 

Followed by i 
20 minutes at 440° Ifurnace cooled 


58.6 
59.1 



IV. CONCLUSION 

The difference in the thermal expansion of alpha and of beta 
brass of compositions which normally are in equilibrium in such 
alloys as Muntz metal, naval brass, etc., has clearly been shown 
by the measurements made. Fundamental variations in be- 
havior as regards thermal expansion at temperatures up to 6oo°C 



590 Bulletin of the Bureau of Standards [Vui.i 4 \ 

were noted, due to the occurrence of a transformation in the beta 
constituent 

The effect of the local or, as they might be called, "grain" 
stresses, on the physical properties and service behavior has been 
only incompletely indicated. Tests showed that stresses of this 
sort produced by quenching commercial drawn 60:40 brass 
1 -inch diameter rod did not cause cracking in mercurous nitrate. 
On the other hand, a lowering of the proportional limit of the 
alloy amounting to about 2000 pounds per square inch resulted 
from this treatment. 

Manufacturers of brass never quench 60:40 brasses; in fact, 
among them there seems to exist a disposition to regard this 
as dangerous practice. However, no definite data other than 
that recorded above are known to the authors, which would 
show clearly the ill effects of such sudden cooling. 

It is found that naval brass or manganese bronze when quenched 
in such a manner as to leave the beta grains surrounded by alpha 
envelopes, is generally both weak and brittle, and the fracture 
intercrystalline, a condition which has been ascribed to the 
alpha envelope. Now it is known that alpha brass is weaker 
than beta, but not more ductile, such that the authors suggest that 
as an explanation for this brittleness may more readily be assigned 
to existence of tangential tensional stresses in the beta grains 
immediately adjacent to the alpha envelope. 

It would appear to the authors that further investigation 
into this general question of the expansion behavior of different 
constituents of other alloys might reveal causes of mysterious 
failures and weakness now considered quite obscure. Such 
materials as hypereutectoid steels, cast iron, type metal, and 
bearing metals contain two constituents. In many cases one 
of these constituents is brittle, a fact which would accentuate 
the effect of local contraction stresses. The authors hope to be 
able to present some data later along these lines, indicating also 
more definitely the physical effect of such stresses. 

Washington, August 15, 191 7. 



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